If we keep matoran and Toa the same height the hewkii/Macku thing won't be weird.

It has been said that Toa can be in relationships, but the core 6 will not between each other.

Jailer and hahli probably won't even become Toa, because TTV said they want to focus on the original six and/or are not planning that far ahead, but if they do become Toa, their romance wouldn't be as condemned as romance between the Mata.

But, matoran were referred to as "little one(s)" by the Toa, and had a much more childlike demanour, especially 01-03, and if they were the same height, it wouldn't come across as a creepy adult-dating-child kind of a deal.